125lc mk1 crank movement

[davslc]

was wandering about movement allowed on the crank of the 125lc mk1 there is no play in con rod up down or side to side ,but you can move the crank side ways by pulling the flywheel slightly , this is only a slight movement but still there , i have no movement up and down in the flywheel , is this ok or a no no .


cheers dav

[billy]

This is not usually the case for 125's as the left side main bearing should have a tight press fit on the crank shaft (unlike the right side where the crank slips in/out of the bearing easily). Sometimes the l/h bearing is sitting EXTREMELY hard on the crank.

I'd guess someone ground/sanded the crank down a few hundreds of a millimeter or so, so that the crank can slip in/out of the main bearing easily. Reason I believe this is because I can't see how the crank would become "worn out", causing a sloppy fit. I don't know if that is impossible though, but I'd say it is very unlikely.. ?

Anyway, sanding the crank down, it's fairly common to do so on motocross engines to make it easier getting the crank out. My brothers CR is just like that and there is a slight sideways play of the crank assembly (around 0,5 mm by the feel of it). No big deal tbh, as long as we're not talking 1+ mm play or so. It IS however a little more kinky deal on an RD as it has angled teeth on the primary/secondary gears, (mx bikes don't, they got straight gears) causing sideway forces of the crank.
You could shim the crank shaft/s to get less sideways play though. Just add a shim that are some 0,1 or so mm thinner then the current sideways play and it'll stay in place, causing no drama.

EDIT: Oh and you could always add some loctite on the crank and inside of inner bearing race as you assemble the stuff. There's loctite designed specifically for these applications. I'm not sure how well it will hold up in the long run though because of the angled teeth of the gears causing sideways load. Worth a try perhaps.

[davslc]

thanks for the info billy will take it all on board when rebuilding it as i will strip and rebuild into my engine casings .

[davslc]

well engine stripped and bottom end rebuilt into my engine casings which had new crank bearings fitted , no sideways play whatsoever now ,no play in crank at all so all good ,just top end to refit now has had recent rebore and piston by the look of it ,happy bunny now .frame and a couple of bits at powder coaters should be back tomorrow all being well .